Intracorporeal leads are in particular used with multisite pacing or re-synchronization devices, to stimulate the left atrial and/or ventricular cavities, depending on the configuration and the location of the lead. These leads are typically equipped with a screw anchor, generally a retractable screw, allowing fixing of the lead head into the wall of the septum, so that the electrode of the distal part of the lead is applied in a manner substantially perpendicular to the wall. Given this setup, the placing of the septal leads is a particularly delicate operation—unlike the placement of right cavity pacing leads which are simply pushed until they reach the apex of the right ventricle. The septal leads are, like the other intracardiac leads, introduced through the venous network, either via the right cephalic vein and the superior vena cava (“right approach”), or via the left cephalic vein and the superior vena cava (“left approach”). In the case of a conventional right cavity pacing lead, the lead is simply pushed to the apex of the ventricle. However, for a septal lead, once the head has reached inside the cavity, the lead distal termination needs to be oriented perpendicularly to the septum wall and pressed against the wall at the selected pacing site so that it can be anchored there by screwing the lead head, including the electrode, into the septum.
To easily guide the distal end at the time of implantation to the selected pacing site, and in a direction substantially perpendicular to it, the lead must be relatively rigid. To do this, the surgeon first introduces a stylet in the form of flexible wire into the hollow, flexible sheath, of the lead body. The stylet is provided at its proximal end, emerging from the lead, with a control handle allowing the surgeon to transmit a rotation and translation movement of the stylet within the sheath. The lead, rigidified by the stylet, can then be introduced in the venous network. Then its distal termination can be oriented by rotation of the handle at the proximal termination of the stylet. In this way, the surgeon rotates the end of the lead head—which presents a curve—and directs it to the septum implant site. Once the site is reached, the surgeon then anchors the lead head by rotation of the screw anchor that penetrates the tissues of the septal wall.
In contrast to right cavity pacing leads, whose positioning is relatively easy (in the ventricle apex), in the case of a lead head to be anchored to the septal wall, the diversity of venous access routes and the cardiac morphology render difficult both the access to the septum and the positioning of the lead head against the septum wall.
To accommodate these features, surgeons attempt to define their own distal conformation of the stylet, by imposing a plastic deformation of the distal end thereof, so as to give the corresponding end of the lead, once inserted into the cavity, a curve facilitating the approach to and docking against the septal wall.
The patent EP1920795A1 (and its corresponding U.S. patent publication US20090105724) describes a stylet having a distal end that consists of an elastic thread preformed using a special three-dimensional configuration, comprising a succession of curved arches facing in different levels. Once the stylet is inserted in the lead, and the stylet/lead combination is introduced into and deployed in the ventricle, this particular configuration allows giving the lead such a shape that it turns naturally in the desired direction. The fine tuning of the distal lead head positioning will be reached by pushing more or less the control handle located at the proximal termination of the stylet. Because of the succession of the various curved arches, the stylet axial movement inside the lead will be transformed in a spontaneous rotation of the latter, without the need to apply and to transmit a torque. Indeed, in this device, the proximal portion is made of a permanently deformable material (so as to give a “memory” to the shape of the stylet), which is not designed to transmit the torque due to its relative plasticity. It is also noteworthy that in this system, all curved conformations of the stylet (and thus of the lead) is located, and used, in the right ventricle, that is to say inside the heart, for the purpose is to enable a fine tuning of the orientation of the lead head by an axial translation of the stylet.
The patent EP 0 778 044 A2 (and its corresponding U.S. Pat. No. 5,807,339) describes an accessory of the “guidewire” or wire guide type, adapted to a particular technique called Over-The-Wire (OTW), in which the guide wire crosses through a probe sheath along its entire length, leading and emerging at the distal end. In reaching its non traumatic end, and to enable its progress directly into a vein safely, the wire guide is terminated at its distal end with a ball or a spire. While returning more or less the guide wire in the probe sheath, it is possible to stiffen it and give it a particular, alterable, curvature to orient more easily in the heart chamber or into the coronary network (but always in the part located inside the heart). A typical application of such a guide wire is the placement of a lead into the coronary sinus by a technique consisting of both to penetrate the core in the coronary sinus and then into the coronary venous system, by gradually sliding the lead over the guide until the final position is obtained.
More complex devices have also been proposed, with two stylets fitting into one another, allowing changing the opening angle of the curved part of the distal end. This solution is relatively expensive and complex, and often unsuitable for the intended function, as it is only possible to change the opening angle of the curved end, not the radius of curvature itself.
In addition, whatever the device used, a typical phenomenon that is well known to physicians during the rotation of the stylet within the hollow shaft of the lead is that, given a gradual rotation of the handle at the proximal end of the stylet, the rotation is translated to the opposite distal end, first by a very gradual rotation of the distal end of the stylet, and, second, after a certain threshold, a sudden jump in rotation of the stylet distal end as the gradual rotation of the handle of the stylet continues. This mechanical relaxation phenomenon results from a progressive accumulation of mechanical torque of the stylet in the lead sheath, followed by a sudden release of these constraints with a jump at the distal end. The jump is felt by the physician in the form of a “clicking” or “rattling” during a rotation of the stylet. This results in an inability to finely control the movement of the distal part of the stylet, and thus correctly directs the lead toward the septum with the required progression and precision.
The origin of this rattle phenomenon is the position of mechanical torque equilibrium of the stylet into the lumen of the hollow shaft of the lead, the latter taking the shape of the venous network in which it was inserted. Insofar as the insertion of the lead, rigidified by the stylet, often leads to permanent deformation of the stylet body, although small, this permanent deformation systematically tries to integrate in the path imposed by the venous morphology (which itself depends on the path, right or left), because of the basic mechanical principle of least energy in torsion.